Photoelectric radio compass trainer control



Oct. 26, 194s. c. J. CRANE 2,452,038

PHoToELEoTRIc RADIO coMPAs TRAINER CONTROL Filed March 12, 1940 4 sheets-sheet 1 rae/Veys Oct. 26, 1948. c. J. CRANE 2,452,038

PHOTOELECTRIC RADIO COMPASS TRAINER CONTROL Filed March 12, 1940 4 sheets-sheet 2 w, U55 T Oct. 26, 1948. c. J. CRANE 2,452,038

PHOTOELECTRIC RADIO COMPASS TRAINER. CONTROL Filed March l2, 1940 4 Sheets-Sheet 3 L/z @ha Oct. 26, 1948. c. J. CRANE PHOTOELECTRIC RADIO COMPASS TRAINER CONTROL Filed march 12, 1940 4 Sheets-Sheet 4 k/Cy v fmwg.

Patented Oct. 26, 1948 PHOTOELECTRIC RADIO COMPASS TRAINER CONTROL Carl J. Crane, Dayton, Ohio Application March 12, 1940, Serial No. 323,561

(Granted under the act of March 3, 1883, as

12 Claims.

amended The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment t me of any royalty thereon.

This invention relates to auxiliary apparatus for use in conjunction with aviation ground trainers and more particularly relates to a means for simulating the radio navigational aid employed in aircraft, known as the radio compass.

Aviation ground trainers for instructing students in the art of instrument flying are well known in the art and such trainers generally comprise a grounded dummy aircraft, tiltably and rotatably mounted on a base and controllable by the occupant in a manner to simulate all of the normal flight maneuvers of an airplane. Various instruments are provided for indicating the flight attitude and the directional heading of the trainer. For a more detailed description of one form of trainer of the type above described, reference may be made to United States Patents No. 1,825,462 and No. 2,099,857 granted to Edwin A. Link, Jr.

It is customary to employ an automatic course indicator, or recorder in conjunction with aviation ground trainers of the type above described, to trace the course of the simulated flight of the trainer on a record sheet such as a chart, or map, representing the trainer over which the simulated ight is taking place. The course indicator, or recorder comprises a frame supported on rollers and movable over the reference surface. The rollers, generally three in number, are each steerable and interconnected by gearing to the receiver unit of an electrical motion transmission, which is electrically connected to a corresponding motion transmitter unit, driven by the trainer as it rotates about a vertical axis. The changes in heading of the trainer thus cause equal changes in heading of the course indicator. Two of the supporting rollers of the course indicator are provided with power driving means consisting of small electric motors geared to the rollers and rotatable with the rollers about their steering axes. The motors drive the course indicator over the record surface at a velocity proportional to the simulated velocity of the ground trainer. The third roller may be inked by a felt pad and record the indicator path on the chart. The position of the marker roller serves the function of an indicator apart from its marking function. For a more detailed description of such a course recorder, or indicator, reference may be had to United States Patent No. 2,179,663 granted to Edwin A. Link, Jr.

April 30, 1928; 370 O. Gr. 757) One form of manually controlled radio compass indicating device for use with an aviation ground trainer and automatic recorder is known in the art and comprises an indicator mounted in the trainer cockpit and electrically connected to a potentiometer mounted on the course recorder, so that the resistance windings thereof, rotate with the marker wheel steering mechanism. The potentiometer has asighting device which is attached to the contact arm of the potentiometer and the instructor must keep the sighting device pointing towards an assumed radio station point on the reference chart. When the movement of the course indicator is along a line directly toward or away from the radio station point, the indicator remains centered, while if the heading is to the right, or left of the station point, the indicator will so indicate, the indications being reversed on movement away from the station point. In order to function properly,

'it is essential, that the instructor continually watch and manipulate the radio compass device and hence cannot devote his attention to other phases of the trainer flight and any errors of observation on the part of the instructor will cause a similar error in the indication given the student in the trainer.

The present invention relates to a means to automatically actuate a radio compass indicator in a ground trainer by photoelectric means so as to relieve the instructor of the duty of manually controlling such an indicator and eliminate the errors attending such manual control.

The principal object of the invention is the provision in an aviation ground training system, of an aviation ground trainer having a radio compass indicator mounted therein, a course indicator directionally controlled by the trainer, a light source located at a point over the recorder reference surface, representing a radio transmitting station and photoelectric means carried by said recorder and connected to the indicator, the photoelectric means cooperating with the light source to indicate the heading of the recorder relative to the source, to thereby simulate the action of a radio compass, as employed in aircraft.

A further object of the invention is the provision of a plurality of light sources over a record table traversed by an aviation ground trainer course indicator, the course indicator having mounted thereon, a photoelectric device, which cooperates with a selected one of said sources to cause a radio compass indicator to indicate the heading of the course indicator relative to the connecting the indicator andathe photoelectricl device, as employed in the device of Fig. 1.

Fig. 4 is a schematic showing of the control system for controlling the various light sourcesemployed in the device of Fig. l andlfuither shows a view of the photo-electric device connected in a;circuitfsuchas,illustrated inFig. 3.

.Fig.,-5 .isa top rplan View of the device of Fig. l illustrating :different ,positions of the recorder relative-.toa given: light sourceand the indicator indications i corresponding vto each position.

,Referringlto Fig. .i 1,-,the numeral I, indicates aniaviationfgroundltrainer ofthe-type above described, tiltablesand rotatable about the base 2, under: theqcontrol ofthe occupantof the trainer. Tfhetrainer I,-has a 'Selsyn` transmitter S, the rotor-.of-which is. rotated bythe traineras it changes its .-headingtand. the Selsyn transmitter-S; is electricallyconnected by a cable Si, with a corresponding Selsyn, receivensz, .mounted on tha. fra-me .ofv the` course recorder,` or Aindicator 5 and connected byrpinion gears I3, to the roller steeringgearsSvand I2, respectively. The course recorder .or indicatorzS, is providedfwith apair of spaced `supporting rollers 6, steerably supported on-verticallshafts, carriedv by the recorder frame.

The. rollers 5,.-are driven. fromsmall electric motors 1, :supplied from an electrical source (not shown) ,i to drive the course indicator, or recorder 5 over `the,s.urface ofthe-record or vchart table 3,at avelocityproportional tothe simulated flight velocity-:.oitrainer-I. yThe Y:motors are mounted on the shafts 8 and are rotatable therewith. The steering-gearsagarefmounted on the upper. ends of-.the. respectiveeshafts 8. A marker roller HJ, isj mountedv `-on za` vertical shaft the-recorder framefzand the-marker` roller-when inked;by.=a felt-pad (notshown), serves to'record the path of the-.recorder ori-a; suitable map placed onthe record table. iThe position of the course recorder is at albumes-indicated by the point of contact. of the marker vwheel-lll, with the record chartonA the table-13 andy hence the term course indicator, generally. applies` tothe Arecorder 5 irrespective, of whetheror .not thev marker wheel I5 is used-.as-a'recording ,means It is thus seen, that the course vindicator 5,-will accurately follow a-:course under' `thedirectional control of the trainerl I, atgavelocity proportional tosome predeterminedrsimulated.velocity of the` trainer.

. ,A Iphoto-electric4 device generally indicated by the reference numeral I5, ismounted on the upper end of the shaft H, of the marker wheel ilLand isrotatablewith thezsha-ft I Land, cooperates with a..commutator..device. generally. indicated -by the referencenumeral. 25, which isf electrically ,connected byf-,acable 30, with vthe radio compass indicator 3|,mounted-dn, thecockpit Vof the trainer I. ,..Thaphotoeelectric device. I5, cooperates with any oneiona,pluralityoflght sourcesy L1, L2, La,

iiepc.,.tq,eause,the. nomenclature indicate, me

I I, supportedy by i instant heading of the course indicator 5, relative to a selected one of the light sources, in a manner hereinafter described. The light sources are small electric exciter lamps, which are mounted as shown on a hood li, which completely encloses the, record. surface of thetabla 3,and prevents external lig-ht; from aecting the photo-electric device i5, and the interior surfaces of the hood ispainted with a light absorbing coating. The light sources L1, L2, etc., are located over desired points on the reference surface 3, so that their location represents the position of various as- .sumed radio transmitting stations on the reference chart. The light sources Li, etc., are each connectedby a cable 45, to a control switch assembly generally indicated by the reference numeral'lil, mounted in the trainer cock-pit, so that afdesiredyoneof the vlight sources may be energized by control from the trainer cockpit. The operation of the switchfcontrol 40, simulates the operation'l of a radiocompass receiver in an actual aircraft night.

lReferring toFigs.2..vand.2A, the photo-electric device I5, comprises a cup shaped container I6, made of. an insulating material and mounted on astem. I I,made ofinsulating material and rigidlymounted-onthe upper end of the marker wheel shaftvII, to rotate therewith. The contemer-I6, has .secured therein a pair of semi-circular `light sensitive cellsv I8 and- I8', respectively, which, have. :output leads I9, IQ and 20, 2U', respectively made in the form of metal lpins secured inthe container I6. The light sensitive surfaces of. the cells are separated bya dividing screen I 1,

which is coated ywith a, black light absorbing coating. The entire .photo-cell -assembly I5, is rotatable with the markerwheelas it changes its headingunder thecontrol .of the trainer I. The lightsensitive cells.employed, are ofthe Well known Weston "Photronic type and are used, because cells of this ,type do not require any battery,.or other power-source, the current duc to photo-electric effects being suicient to actuatc a .sensitivewmeter withoutthe necessity of any external lbattery. It is -to be understood, however, that-any other ltypephoto-cell vsuch as alkali metal. or selenium cells =may bev used, employing, the .usual .battery source in conjunction therewith. The term .photo-cell as Aused herein, is intended: to be generic to both types of cells.

,Amercurycontactor device, or commutator device, generally indicated at 25, compri-ses a, circular ,block-of insulating material, secured to the frame` of the course indicator 5 and having four annular channelsZt, 27, 28 and 29, formed therein, concentric with the-,axis of the 1marker wheel shaft II. The channels 26, 27,\etc., are each filled With mercury to. such a depth, that one of the respective leads I9, I9', 20 and 20' will be partially immersed therein. The conductor pins I9 and Ill', dip, in the: mercury contained in the annular channelsy 2S1and2't respectively and the conductor pins 20 and. 2li', respectively, dip in the mercuryy contained yin the annular grooves 28 and 2.5. `I'hemercury in each of the annular grooves 25.2l,-28and29, is respectively in contactfwith conductors` 32, 33, 34 and 35, which are connected inthe form of a cable Sil, tothe radio compass findicatorl, of Fig. l. It is thus seen, that by meanssof the commutator device 25, the current generated -by photronic cell I 8, may pass by Way of `conductor pins I9 and I9', to leads 32 and-33v and similarly, current generated by photronicc cell ifgmayipasscby Way of conductor pins 20 and 20', to the conductorsgidand:by

means of the mercury in the grooves 26, 21, etc., with a minimum of electrical resistance, but permitting free rotation of the photo-cell assembly I5, with the marker wheel shaft I I.

.As seen in Fig. 3, the positive conductor pin I9, of photronic cell I8, is connected by conductor 32, to the lead 35, connected to the negative conductor pin 26', of the photronic cell I8. Similarly the negative conductor I9', of photronic cell I8, is connected by conductor 33, to the lead 34, connected to the positive conductor pin 20, of cell I8'. Extensions of leads 34 and 35, are connected to the terminals of a sensitive zero center type meter 3l. By inspection of the circuit, it will be seen, that the cells I8 and I8', are connected to each other in series and in electrical opposition, so that if each cell is producing a current of equal magnitude there will be no potential difference existing between the extended leads 34 and 35, connected to meter 3|, and the indicator pointer will remain centered, If cell I8, delivers a current greater than cell I8', a current will ow through the indicating meter 3|, in one direction, causing the pointer to deflect in one direction, for example to the left, while if cell I8', delivers the greater current the current iiow through the indicator meter 3|, will be in the opposite direction and the pointer will then deflect to the right. Since the current generated by a photronic cell is proportional to the intensity of light falling upon it, the cells I8 and I8', will generate equal currents when the same intensity of light strikes each cell and hence under such conditions, the pointer of indicator 3| will remain centered as described above. If cell I8, receives light with a greater intensity than cell I8', the pointer of indicator 3I, will deect to the left and similarly if cell I8', receives the greatest amount of light, the pointer will dei-lect to the right. The pointer deflections may be reversed from that above described by simply reversing the connections to indicator meter 3l, or a reversing switch may be used.

As seen in Fig. 4, the various light sources, or exciter lamps L1, L2, La, etc., each have one lament terminal respectively connected to one of the points 42, of a rotary switch 45 and the other filament terminals are each grounded to a power supply lead 49. The other power supply lead 48, is connected through rheostat 56 to the rotatable switch arm 43. The switch arm 43, is rotated by a shaft 44', turned by a control handle 46, which also serves as a pointer to cooperate with the dial 41, which is provided with suitable indicia, to indicate the particular exciter lamp being energized from the power supply leads 4B and 49, which are adapted to be connected to a suitable power source, preferably of the direct current type (not shown). The rotary switch 45, dial 41 and control handle 46, are mounted as a unit 46, in the cockpit of the trainer I, as illustrated in Fig. 1. The construction of the rotary switch 45, as seen in Fig. 4, is such that only one exciter lamp may be energized at any one time; and this is essential, since if more than one exciter lamp is lighted, the co-mingling of the light from the two sources will give a resultant light distribution such that under certain conditions the apparent source of radiation would be at some point other than at either of the actual sources of light, thus giving rise to erroneous results. The operation of the switch 45, by turning the control handle 45, to select the desired exciter lamp representing the desired radio compass station, simulates the tuning of a radio compass receiver to a particular station, which in actual ightis to serve as the desired radio compass homing, or bearing station.

-As best seen in Fig. 2 the exciter lamps L1, etc.,

are each encased in a suitable protecting casing 5I, having a transparent portion 52, extending within the hood 4 and the casing is provided with small colored bulls eye lens 52' located externally of the hood 4, so that the respective light source being energized will immediately be apparent to the instructor. If desired, a remote indicator may be actuated by the shaft M, of the switch unit 46, tov indicate the respective light source being energized.

Fig. 4 further illustrates the connection of the photo-cell device l5, to the indicator 3l, the connections illustrated in Fig. 3 between the 32,33, 34 and 35, actually being made at the indicator 3 I so as to be readily accessible, the leads 32, 33, 34 and 35, being enclosed in the cable 36, previously described. f

Operation Thev operation of the photo-electric radio compass for ground trainers, above described, can best be seen by reference to Fig. 5, which schematically illustrates a top plan view of the record table 3, which has the hood ll, placed over a por tion thereof. A suitable chart, or map C, is placed on the record table and the vertical lines passing through the various light sources L1, L2, etc., intersect the chart at positions representing various cities, which may be desired destinationsy and assumed to be radio station broadcasting points for use in homing with the radio compass indicator. The various assumed positions of the course indicator 5, during operation, are indicated as positions P1, P2, and P3, respectively. The deilectionsoi the indicator 3l, for the various course indicator positions, are indicated in the indicator illustrations P1, Pz, Ps, above the table 3.

Assuming that the simulated destination is Cincinnati represented by exciter lamp L1, and that the course indicator 5, is in operation with the heading indicated by the plane of rollers 6 and the light dividing screen Il. The student deu siring to home towards Cincinnati, actuates the switch control 40, in the trainer cockpit to energize exciter lamp Li. It will be seen that in po sition P1, light radiated from exciter lamp L1, will strike photronic cell lil, without hindrance but will be partially shielded from photronic cell i8', by the dividing screen il" and since cell i8, receives light of greater intensity than cell I8', the pointer of indicator SI, will deflect to the left as above described with reference to Fig. 3. It is thus seen that the indicator 3l, will correctly indicate the heading of the course indicator and trainer relative to the assumed radio compass transmitting station .represented by the point on the chart directly beneath exciter lamp L1. 'The course indicator may then be considered in operation in position P2 and it will be seen, that the heading as indicated by the plane of the rollers 5 and dividing 'screen il, is such.. that the photronic cells i6 and it', will receive light with equal intensity and for reasons as stated above, with reference to the description of Fig. 3, the pointer of indicator di, will 'be centered., indicat ing that the course is directly towards the assumed radio compass station. Similarly `in position P3, the cell it', will receive light with a greater intensity than cell i8 and the pointer of indicator 3i, will deflect to the right, indicating that Ithe course indicator is heading to the right of the assumed radio compass station point representedacrr. the: chart rby Cincinnati. It will benot- .edsfthat in-jthevariousLpositions PhyPz; for: Pa, the .indication .-Will bev thesame; regardlessof whether 4the; coursei :indicator is .moving alongzxtsiheadmg '.axisfeither toward; or'fawayj from, thezassumed :radio ycompass transmitting nstation Cincinnati Yand linzorder to determine the position of. the-assumed transmitting; station, the "trainer .is turned -.to `the right and'. it the indicator pointer` deflects 'towardthe rightffrom its instant position the staftion lis rahead in' the"direction of 'motion-ofthe v.course indicatorawhile if .the deflection isftol the left the assumed transmitting stationis to the reareinthe direction of motion fromthe course indicator. Theauthorities--are not agreed` onrthe relation beiuvveeny pointer-deection and direction ,of heading torthe right or left of` the radiov compassistation.' and` theI left .and right deflections may.' be. interchanged lby .simply reversing thek 4indicator connections, so as to agree with conventions of the navigatingssystem being used.

The student during the `trainer flight, attempts ,tofmaintainthe trai-ner.` heading such, that'vthe radio'compass indicator pointer remains centered, after determinationeof the sense of the direction `oflight transmissionA to1 .determi-nef whether. the .direction ofv the. simulated -iiightY is directly' towards, ors-away from theiassumed transmission station point. As thelcourse indicator approaches the vertical axis of the-light source, the sensitivity ,30

.of the indicator for a given deviation from thetfon course heading is greatlrr increased, since the light `intensity will vary. inverselyas the square. of the distance. from the lightrsource. -Byproper selection of the typefof the-exciterflam-ps and proper `adjustment of their vertical height labove the reference table surface, the light distribution may be madevsuchythat its reffect on the photronic cells will closely simulate the variation insignal intensity with .distance from the transmitting station, experienced in actual aircraft night and the radiation of light-Will .under .proper control be substantially-equal in, all directions in-a horizontal plane, duplicating the `non-directional.radiation of the radio waves from radio compass transmit- Y ting.- stations, which very often are the ordinary radio broadcastingV stations.

In order to simulate the actuation of the volums-control of a radio compass receiver to obtain .an-approximate ideaiof distance from the transmitting station,-a rheostat 5l)` is inserted in the power supply circuit i3- 49, for the various exciter lamps L1,-L2, etc.,. as illustrated in Figufi. The rheostat is preferably mounted in the cockpit of the trainer so. that `its control knob isdn close proximity to the exciter lamp selector switch control-dB-and by control oftherheostat .the intensity of light radiated bythe selectedone'oi the exciter lamps L1, L2, etc. can be controlled by the student so that the deiiection of the pointer of the indicator 3|, may be controlled similar to the'effect of varying the receiver volume in an actual radio compass 'system employed -onfan aircraft. As the course -indicatoriiapproaches the light ,source selected'- to represent the desired transmitting station, the pointer of indicatorl, .will deflect an ever increasing amount, for -a givensmall deviation from a heading directly towardsthe .chosen light source. If thestudent then reduces the intensity of light radiated, by the active exciter 'lamp by actuating the rheostat control 50, so that the pointer deflection remains constant at some selected -value, the amount the knob of. rheostat-EU, is moved, may be interpreted irl-terms. of distance from; the transmittingrstation, in the same. manner'fasddistance iromthe transmitting station is approximated by actuation of the volume control of the radio compass receiver by an aircraft pilot.

-The radiofcompass simulatingsmeans above .described, may be used to home `on anyone ofthe .various 'destinations f represented -by the various exciter lampsy and the apparatus will'faithfully reproduce indications simulating an actual radio compass .as .used in aircraft navigation. :The photo-electric radio-compass f o1'` aviationground trainers above described may also' be usedtin vsimulatedrblind?landings#vvith' `.the .trainer-r where two alignedvlight -sources may 'be employed ina 'mannerftoesimulate the ltvvo radio compass stations aligned with the landing runway,'employecl inr tlie;-Arrny Air 'Corps v Blind' Landing-System. 'TheV two faligned flight sources are `respectively :mountedfdirectly Labove pointsonthe reference suriacespaced at .predetermined distances'from :a fpoint ron i the .a said Asurface representing the boundary -cf an'assurned airport'ianding runway; andsthelight sources; as abovenotedzare-aligned with the axis ofthe simulated iandingsrunwayon the "record chart. Theflight sourceshenrespectively represent .the inner andi-outery radio compass transmitter stationsxemployed' inthe above-notedtArmy Air Corps' Blind Landing Sys- `tenu-and*the-studentin the trainermay then simiuiate "flight toward either the inner or theouter radio Vcompass station' by: energizingY the" correspond-ing r exciter Ylamp and maintaining the trainer heading@ such that the "course indicator heads` towards vthe selected station `point on' the lrecord chart, the deviation from thes-properhead- 'ngbeing indicated by the indicator 3l. The lcourse-indicator may bedirectiona'lly aligned-With the :axis off the landing runway-on thev record -chart /and'moving--in directionsuch as to .make a proper simulatedlandingby the procedure out- .Jined -in :the icopending application Serial "No. -32087 9, `iiled-'liebruary 26, 1940; for improvements in Blind flying and blind landing system for aviationflight trai-ner; in the 'na-mes of. CarlfJ. Crane, .George-V.--Holloman,Carl fWJMuller, and -Raymond. K.: Stout, .whichY application also disc-loses the use'of 4marker beacon simulating Nsignals energized by the recorder when arrivingat the respectiveradio compass station pointsand formfing one of they essential features used in combinationfwithradio compass simulating means 'tor making'a simulated instrument landing in accordance-With the Army Air Corpssystem. LIheflight procedureqforcarryingfout an instruyment landing in accordance 'with' the-Air Corps System is'fully-,described and illustrated-in the .Air Commerce-Bulletin of the'y U; S.' Department or Commerce, vol. d,v No. 5,y entitled Army Air Corps- Radio. VBlindl Landing System -Adopted as Standard. While :one form of the invention has been illustrated"and'des'cribed, modilications willy becca e apparent'ito thoseskiiledV in the art.' falling-Within thescope. of the invention as defined bythe appended claims. I

'I claim:

L'In. combination, an aviation ground trainer for simulating the flight-of an aircraft, a reference'surface, a course indicator movable relative to said `reference surface at a velocity proportional to the simulated velocity in flight of said aircraft and directionaily controlled by said trainer, a light source for radiating light over said reference surface symmetrically'with respect to a point 4onsaid reference surface representing the location of a simulated radio station, a photoelectric devi-ce mounted on said course indicator and controlled by indicator to receive light transmitted from said source in accordance with the heading of said course indicator relative to said simulated radio station point on said reference surface, an indicator in said trainer electrically connected to said photo-electric device for indicating the heading of said course indicator relative to said simulated radio station point.

2. The structure as claimed in claim 1, in which the said indicator is mounted in said trainer.

3. The structure as claimed in claim 1, in which the light source comprises one of a plurality of exciter lamps, each of said lamps being mounted directly over a point on said reference surface representing an assumed radio station and selector means mounted in said trainer for selectively energizing one of said excited lamps.

4. The structure as claimed in claim 1, in which the said indicator is mounted in said trainer and in which the light source comprises one of a plurality of exciter` lamps, each of said lamps being mounted directly over a point on said reference surface representing an assumed radio station and selector means mounted in said trainer for selectively energizing one of said exciter lamps.

5. The structure as claimed in claim 1, in which the said photo-electric device includes a pair of light sensitive cells each electrically connected to said indicator and a rotatable screen directionally controlled by said course indicator in response to changes in heading thereof to vary the quantity of light received by each of said cells to thereby vary its respective effect on said indicator.

6. In combination, a reference surface, a course indicator movable relative to said reference surface and having a controlled motio-n so as to indicate the course of a desired object such as a vehicle, a light source arranged so as to radiate light over said reference surface symmetrically with respect to a predetermined point thereon, a photo-electric device carried by said course indicator, an electrical indicator connected to said photo-electric device for indicating the direction and approximate magnitude of the deviation of said course indicator from a heading directly towards or away from said point on said reference surface and light shielding means for varying the quantity of light received from said source by said photo-electric device in response to deviation of said course indicator from said heading directly towards or away from said point on said reference surface.

'7. The structure as claimed in claim 6, in which the photo-electric device includes a pair of light sensitive cells and in which said shielding means is a light dividing screen rotatable in accordance with the change in heading of said course indicator from said heading directly towards or away from said point to thereby vary the quantity of light received by each respective cell.

8. The structure as claimed in claim 6, in which the photo-electric device comprises a pair of photronic cells rotatably mounted on said course indicator and directionally controlled by said course indicator and a light dividing screen rotatable with said photronic cells for varying the amount of light received by each of said cells.

9. A radio compass simulating device for aviation ground trainers comprising, a reference surface, a light source for symmetrically radiating light over said surface with respect to a predetermined point thereon, a pho-to-electric device movable relative to said reference surface, an indicator electrically connected to said photoelectric device and a means for varying the quantity of light received from said source by said photo-electric device to cause said indicator to indicate the deviation of said photo-electric device from a heading directly towards or away from said predetermined point on said reference surface,

10. The structure as claimed in claim 9, in which the photo-electric device includes a pair of light sensitive cells each electrically connected to said indicator to cause actuation thereof in opposite directions with a torque proportional to the amount of light received by each cell, the net deflection of said indicator representing the effect of the deviation of said photo cell device from the said heading directly towards or away from the point on said reference surface, and a light dividing screen mounted between said cells and movable therewith to cause a difference in the amount of light received by said cells in response to the said deviation in heading of said photo-electric device.

11. The structure as claimed in claim 1, including a means mounted within said trainer for selectively controlling the intensity of light transmitted from said light source.

12. In combination, an aviation ground trainer universally pivotally mounted for movements simulating those of the flight of an aircraft, a reference chart surface, a course indicator movable relative to said reference surface at a velocity proportional to the simulated velocity in night of said aircraft and directionally controlled by the movement of said trainer, a light source for radiating light over said reference surface symmetrically with respect to a point on said reference surface representing the location of a simulated radio station, a photo-electric device mounted on said course indicator and controlled by said indicator to receive light transmitted from said source in accordance with the heading of said course indicator relative to said simulated radio station point on said reference surface, an indicator in said trainer electrically connected to said photo-electric device for indicating the heading of said course indicator relative to said simulated radio station point.

CARL J. CRANE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,825,462 Link Sept. 29, 1931 2,099,857 Link Nov. 23, 1937 2,119,083 Link May 31, 1938 2,164,412 Koster July 4, 1939 2,179,663 Link Nov. 14, 1939 OTHER REFERENCES Air Corps News Letter; voi. 21, No. 6, March 15, 1938, pages 7-8.

Aeronautics Bulletin No. 27, July 1, 1937, published by the Bureau of Air Commerce of the U. S. Dept. of Commerce, pages 26-29. 

